Hi Marc,
"Canadian brown", or actually British(!) Standard Camouflage Colour (S.C.C.) no.2 was in use from early 1942 until early 1944 as the base tone for vehicles. I'd paint it in that colour, alternatively, if you like green better make sure you use S.C.C. no.15 Olive Drab instead of the U.S. Olive Drab. For more info see
http://www.mafva.org.uk/Resources.asp
The attached pic shows you trailer, right?
Regard,
Hanno